Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.66   4.308%   $256.243   $256.24   $256.25   $256.20  
  Purchase #2 $35.44   3.762%   $36.7733   $36.77   $36.75   $36.80  
  Purchase #3 $176.28   3.275%   $182.0532   $182.05   $182.05   $182.10  
  Purchase #4 $239.45   4.299%   $249.744   $249.74   $249.75   $249.70  
  Purchase #5 $56.57   13.744%   $64.345   $64.35   $64.35   $64.30  
  Purchase #6 $178.89   11.778%   $199.9597   $199.96   $199.95   $200.00  
  Purchase #7 $187.30   3.658%   $194.1514   $194.15   $194.15   $194.20  
  7 purchase totals = $1,119.59       $1,183.2696   $1,183.26   $1,183.25   $1,183.30